The present invention relates to a system and method for detecting materials concealed within, or on, a vehicle, particularly for inspecting a vehicle when personnel are present within, and driving, the vehicle.
It is desirable to determine the presence of objects, such as contraband, weapons, or explosives, that have been concealed, for example, in a moving vehicle, or, additionally, under the moving vehicle, in either case, without requiring the subjective determination of a trained operator. The determination should be capable of being made while the container is in motion, indeed, as inspection rate and thus hourly throughput is at a premium, it is desirable that the vehicle be driven without requiring the driver or passengers to alight. In case a detection is made, a visual image should be available for verification.
The use of images produced by detection and analysis of penetrating radiation scattered from an irradiated object, container, or vehicle is the subject, for example, of U.S. Pat. No. 4,799,247 (Annis et al.) and U.S. Pat. No. 5,764,683 (Swift et al.), where are herein incorporated by reference. The techniques taught in these patents require that the motion of the inspected object relative to the source of radiation be at a controlled rate, either by moving the inspected object on a conveyor, by sweeping the orientation of the source, or by mounting both source and detector arrangement on a single movable bed and driving them past the inspected object at a known or determinable rate.
UK Patent (issued from Application 2 277 013, filed Mar. 31, 1994) to Bermbach teaches the examination of a loaded truck by driving it through an examination bay while irradiating one side with a fan beam of low-energy x-rays while detecting the x-rays transmitted through the truck with detectors formed from an angular strip. The detectors are taught to be formed from a series of detector elements such that their output signals may be converted into an image of the relevant irradiated zone of the truck.
U.S. Pat. No. 5,917,880, to Bjorkholm, issued Jun. 29, 1999, teaches moving a vehicle on a conveyor at a regulated speed through a bay in which it is illuminated by a fan beam of high-energy x-rays in the range of 1-8 MeV, the high energy being required so that the x-rays fully traverse the vehicle and its cargo for detection, on the opposite side of the vehicle, of forward scattered radiation.
Another system for using x-rays transmitted through a moving vehicle, such as a moving railway car or other large shipping container, has been taught in U.S. Pat. No. 5,910,973, to Grodzins, issued Jun. 8, 1999, and incorporated herein by reference. Grodzins taught embodiments wherein transmitted x-rays are detected by one or more detectors placed on the side of the car distal to the source of irradiation. Disadvantages of the inspection systems based on transmitted x-rays include their typical insensitivity to organic materials having low attenuation, especially those in sheet form, and, especially, the requirement that sufficiently energetic x-rays be used to penetrate the entire thickness of the inspected vehicle. This makes a transmission-based inspection system inappropriate for the inspection of automobiles, and may also limit other applications due to the implicit safety threat to humans who are either known to be in the vehicles or else concealed there.
In accordance with one aspect of the invention, in one of its embodiments, there is provided an inspection system for inspecting a moving vehicle. The system has a source of radiation for providing a beam of penetrating radiation of specified cross-section directed in a beam direction substantially horizontal and transverse to the direction of motion of the vehicle. Furthermore, the system has a detector arrangement disposed between the source of radiation and the moving vehicle for detecting radiation from the beam scattered by any material disposed within the moving vehicle and for generating a scattered radiation signal, and a controller for characterizing the material disposed within the moving vehicle based at least on the scattered radiation signal.
In accordance with various embodiments of the invention, the inspected vehicle may be a train car, an automobile, or a truck. The source of penetrating radiation may be an x-ray source, and the source of penetrating radiation may include a beam scanning mechanism such as a rotating chopper wheel or an electromagnetic scanner. The beam itself may be shaped as a pencil beam.
Alternate embodiments of the invention may additionally have a second source for providing a second beam of penetrating radiation of specified cross-section directed in a second beam direction transverse to the direction of motion of the vehicle and a second detector arrangement disposed between the second source of radiation and the moving vehicle. The inspection system may also have a display for displaying a scatter image of the material disposed in the interior of the vehicle and a processor for associating pre-stored characteristics of the vehicle such that the scattered radiation signal may be compared with the pre-stored characteristics. Additionally, the inspection system may have a velocity sensor for registering the velocity of the vehicle with respect to the inspection system.
In accordance with yet further embodiments of the invention, the beam of penetrating radiation may have a variable energy spectrum and the controller may characterize the material disposed inside the vehicle based at least on combination of the scattered radiation signal under conditions of illumination with a first energy spectrum and the scattered radiation signal under conditions of illumination with a second energy spectrum.